The invention relates to the general field of aviation. In particular, the invention relates to monitoring a filter of a circuit for feeding fuel to an aircraft engine.
In known manner, the fuel feed circuit of an aircraft engine is provided with a filter for capturing particles present in the fuel by means of a porous filter element. Such capture modifies the porosity of the filter element and that gives rise, under constant operating conditions, to the pressure difference across the filter increasing as a function of time.
That phenomenon is referred to as “clogging”, and it increases the resistance of the filter to passing fuel. Clogging can take a shorter or longer length of time depending on the amount of pollution to which the filter is exposed. Clogging caused by particles present in the fuel is referred to as “normal” clogging or as “extreme” clogging depending on the quantities and the types of the particles.
In the event of normal or extreme clogging, it is appropriate to replace the filter element of the filter. It is thus known to measure the head loss across the filter with a pressure difference sensor in order to detect that clogging has occurred. When the head loss across the filter exceeds a certain limit, referred to as the “pre-clogging” threshold, the system is programmed to issue an alarm indicating the need for a maintenance operation.
Furthermore, in the event of clogging being detected, it is also known to open a bypass duct that short-circuits the filter so as to enable fuel to continue to flow through the circuit. Opening takes place automatically as soon as the pressure difference across the terminals of the filter exceeds a certain threshold value (bypass opening threshold) that is higher than the threshold for triggering the issuing of the pre-clogging alarm. When the bypass duct is open, the circuit downstream from the filter is subjected to pollution and it is necessary to perform maintenance that is more burdensome, e.g. removing the engine and cleaning the fuel circuit.
Document FR 2 705 734 describes a monitoring method of the above type, in which an alarm message is issued when the head loss across the filter, corrected by the fuel flow rate, exceeds a predetermined threshold.
Furthermore, it is difficult to avoid water being present in the fuel feed circuit. Unfortunately, in an aircraft, the pressures and the temperatures that might be encountered during a flight can lead to water going to the solid state. Under such icing conditions, clogging of the filter may also be caused by ice.
In the above-mentioned techniques of the prior art there is no way of distinguishing between normal clogging, extreme clogging, and ice clogging. An alarm is thus generated even in the event of ice clogging, with that having the consequence of a maintenance operation always being performed, even though such an operation is not necessary if the clogging is ice clogging.